1. Field of the Invention
The present invention relates to the technical field of an Al alloy thin film for semiconductor device electrodes and a sputtering target to deposit the Al film by sputtering process for semiconductor device electrodes. Particularly, the present invention relates to the technical field of an Al alloy thin film for semiconductor device electrodes suitable as electrodes (thin film electrodes and interconnections) of a thin film transistor-liquid crystal display, and a sputtering target to deposit the Al film by sputtering process for semiconductor device electrodes.
2. Description of the Related Art
Liquid crystal displays (referred to as xe2x80x9cLCDSxe2x80x9d hereinafter) as semiconductor devices permit decreases in thickness, weight, and power consumption, and the formation of an image with high resolution, as compared with conventional display devices comprising cathode ray tubes. Therefore, LCDs are used displays for television sets and personal computers, etc. In recent years, a thin film transistor-liquid crystal display (referred to as xe2x80x9cTFT-LCDxe2x80x9d hereinafter) having a structure in which a thin film transistor (referred to as xe2x80x9cTFTxe2x80x9d hereinafter) is incorporated as a switching element for each LCD pixel has become the mainstream. The TFT represents an active element comprising a semiconductor thin film, and electrodes (thin film electrodes and interconnections) comprising metal thin films connected to the semiconductor thin film. Therefore, the semiconductor device electrode is defined as an electrode (a thin film electrode or interconnection) used as a part of TFT. In a TFT, the electrode and interconnection are electrically connected.
A thin film (referred to as an xe2x80x9celectrode thin filmxe2x80x9d hereinafter) used for an electrode of the LCD is required to have various properties, and especially low electrical resistivity, high hillock resistance, high void resistance, and high corrosion resistance are considered important. These characteristics are considered important because of the following reasons.
[1] The reason why low electrical resistivity is required is first described. The electrical resistivity of a material used as the LCD electrode thin film affects the transmission rate of an electric signal transmitted through the material. For example, the use of a material having high electrical resistivity as the electrode thin film causes a decrease in the transmission rate of an electric signal, and thus causes deterioration in the display performance of LCD due to an electric signal delay. Therefore, low electrical resistivity is required for preventing the occurrence of such an electric signal delay.
[2] Next, the reason why high hillock resistance (meaning that no hillock occurs by heat treatment) is required, and the reason why high void resistance (meaning that no void occurs by heat treatment) is required are described. After the deposition of the electrode thin film, the electrode thin film is annealed at about 300 to 400xc2x0 C. in the LCD manufacturing process. This is because of the presence of a step requiring heating, such as the step of forming a Si semiconductor layer, after the deposition of the electrode thin film. For example, in the use of a material having poor hillock resistance and void resistance, such as a pure Al thin film, for the electrode thin film, the heat treatment causes small convexities such as hillocks (protrusions caused by compressive stress as driving force due to a difference in the thermal expansion coefficient between a substrate and a thin film), or small concavities such as voids (recesses caused by compressive stress as driving force due to a difference between the thermal expansion coefficients of a substrate and a thin film) on the surface of the thin film. Conventionally, the electrode thin film is located at the bottom of the multilayer structure of LCD, and thus the occurrence of hillocks or voids causes a problem in which other thin films cannot be evenly laminated on the electrode thin film. In addition, when an insulating thin film is laminated on the electrode thin film, the hillocks produced on the electrode thin film protrude the upper insulating thin film to cause a problem in which an electric short circuit (electric insulation failure) occurs between layers. Furthermore, the occurrence of the voids on the electrode thin film causes the problem of producing an electrical disconnection (conduction failure) in the peripheries of the voids. Therefore, high hillock resistance and void resistance are required for preventing these problems.
[3] The reason why high corrosion resistance is required is finally described. A material used as the LCD electrode thin film is exposed to an alkaline solution such as a photoresist developer in a photolithographic step after the deposition of the electrode thin film. For example, in the use of a material having low corrosion resistance against the alkaline solution for the electrode thin film, the electrode thin film is corroded with the alkaline solution to deteriorate the precision of the electrode shape. The deterioration in precision of the electrode shape causes an electrical short circuit or disconnection in the electrode thin film. Therefore, high corrosion resistance against the alkaline solution is required for preventing the precision of the electrode shape from deteriorating due to corrosion.
As the material for the LCD electrode thin film, (1) a Ta thin film, (2) a Ti thin film, (3) a Cr thin film, (4) a Mo thin film, and the like are conventionally used. Also, (5) an Alxe2x80x94Ta alloy thin film, (6) an Alxe2x80x94Ti alloy thin film, and the like proposed by the inventors in Japanese Unexamined Patent Publication No. 5-100248, (7) an Alxe2x80x94Fe system (at least one of Fe, Co, Ni, Ru, Rh, Ir, and Nd) alloy thin film, and the like disclosed in Japanese Unexamined Patent Publication No. 7-4555 are used. Furthermore, the inventors proposed (8) an Alxe2x80x94Nixe2x80x94Y thin film (Japanese Unexamined Patent Publication No. 11-3878).
The material used for the LCD electrode thin film is required to have severe characteristics by the recent trend toward a larger LCD screen and higher resolution. Particularly, lower electrical resistivity, higher hillock resistance, higher void resistance, and higher corrosion resistance are required. However, the conventional materials for electrode thin films cannot satisfy all requirements. This will be described in detail below.
[1] The shape of the LCD electrode thin film tends to be further made fine with increases in the LCD panel size and resolution. Making fine the shape causes an increase in the electric resistance of the electrode portion and interconnection portion, and an electric signal delay due to this increase in electric resistance causes a great difficulty in improving the LCD display performance. In order to prevent such an electric signal delay accompanying the formation of the electrode thin film having a finer shape, for example, in a LCD having a panel size of 10 inch or more, the electrical resistivity of the electrode thin film must be decreased to 6 xcexcxcexa9cm or less. However, (1) a Ta thin film has an electrical resistivity of about 180 xcexcxcexa9cm; (2) a Ti thin film, an electrical resistivity of about 80 xcexcxcexa9cm; (3) a Cr thin film, an electrical resistivity of about 50 xcexcxcexa9cm; (4) a Mo thin film, an electrical resistivity of about 50 xcexcxcexa9cm. Furthermore, (5) an Alxe2x80x94Ta alloy thin film and (6) an Alxe2x80x94Ti alloy thin film have an electrical resistivity of about 10 xcexcxcexa9cm. It is thus very difficult to use these materials as the LCD electrode thin film required to have an electrical resistivity of 6 xcexcxcexa9cm or less.
[2] The number of heat treatments at about 300 to 400xc2x0 C. which are applied to the electrode thin film in a step after the deposition of the electrode thin film in the process for manufacturing LCD is not limited to one, and the heat treatment is repeated a plurality of times. Therefore, high hillock resistance and high void resistance are required for preventing the occurrence of hillocks or voids even when the heat treatment at about 300 to 400xc2x0 C. is repeated. However, an Alxe2x80x94Nd alloy thin film as (7) an Alxe2x80x94Fe system (at least one of Fe, Co, Ni, Ru, Rh, Ir, and Nd) alloy thin film produces neither hillock nor void in one time of heat treatment, but produces hillocks or voids in not less than two times of heat treatments in some cases, thereby causing difficulties in using as the LCD electrode thin film.
[3] Furthermore, the photoresist developer used in the photolithographic step after the deposition of the electrode thin film in the process for manufacturing LCD is a strong alkaline solution, and thus high corrosion resistance against the alkaline solution is required. However, an Alxe2x80x94Co alloy thin film and Alxe2x80x94Ni alloy thin film as (7) the Alxe2x80x94Fe system (at least one of Fe, Co, Ni, Ru, Rh, Ir, and Nd) alloy thin film, and (8) the Alxe2x80x94Nixe2x80x94Y alloy thin film are corroded by exposure to the strong alkaline photoresist developer, particularly an organic alkaline photoresist developer, to deteriorate the shape precision of the electrode. It is thus difficult to use these materials as the LCD electrode thin film.
As described above, the conventional materials for the electrode thin films cannot satisfy all of the requirements (low electrical resistivity, high hillock resistance, high void resistance, and high corrosion resistance) for the electrode thin films of large-size LCD and high-resolution LCD. Therefore, there have not yet been materials suitable for LCD electrode thin films, i.e., materials for electrode thin films having low electrical resistivity, high hillock resistance, high void resistance, and high corrosion resistance.
The present invention has been achieved with attention to the above circumstances. An object of the present invention is to solve the above-described problems of conventional materials, and provide an Al alloy thin film for a semiconductor device electrode having low electrical resistivity, i.e., 6 xcexcxcexa9cm or less, high hillock resistance, high void resistance, and high corrosion resistance against an alkaline solution, all of which are requirements for an electrode thin film of large-size LCD or high-resolution LCD. Another object of the present invention is to provide a sputtering target to deposit the Al film by sputtering process for a semiconductor device electrode.
In order to achieve the objects, the present invention provides an Al alloy thin film for a semiconductor device electrode, and a sputtering target to deposit the Al film by sputtering process for a semiconductor device electrode, which have the following construction.
The Al alloy thin film for a semiconductor device electrode of the present invention has excellent corrosion resistance, hillock resistance and void resistance, and an electrical resistivity of 6 xcexcxcexa9cm or less, and comprises as alloy components 0.3 at % or more of Y, and at least one of the IVa group metal elements (Ti, Zr, and Hf) in a total of 0.2 at % or more, wherein the contents of Y and the IVa group metal element satisfy the following equation (1):
0.3Cy+3CIVaxe2x89xa62xe2x80x83xe2x80x83Equation (1)
In the equation (1), Cy represents the Y content (at %), and CIVa represents the content (at %) of the IVa group metal element.
The Al alloy thin film for a semiconductor device electrode of the present invention is deposited by a sputtering process.
In the Al alloy thin film for a semiconductor device electrode of the present invention, Y is partly or wholly precipitated as an intermetallic compound with Al, and the IVa group metal element is partly or wholly precipitated as an intermetallic compound with Al, and the intermetallic compounds are precipitated by applying heat treatment to the Al alloy thin film.
The Al alloy thin film for a semiconductor device electrode of the present invention has corrosion resistance against an alkaline solution. The Al alloy thin film for a semiconductor device electrode of the present invention has hillock resistance against repeated heat treatments, and void resistance against repeated heat treatments. The Al alloy thin film for a semiconductor device electrode of the present invention is used for an electrode of a liquid crystal display.
The sputtering target to deposit the Al film by sputtering process for a semiconductor device electrode of the present invention comprises an Al alloy comprising as alloy components 0.3 at % or more of Y, and at least one of the IVa group metal elements (Ti, Zr, and Hf) in a total of 0.2 at % or more, wherein the contents of Y and the IVa group metal elements satisfy the following equation (2):
0.3Cy+3CIVaxe2x89xa62xe2x80x83xe2x80x83Equation (2)
In the equation (2), Cy represents the Y content (at %), and CIVa represents the content (at %) of the IVa group metal element.
In the sputtering target to deposit the Al alloy thin film by sputtering process for a semiconductor device electrode of the present invention, the Al alloy is produced by a melt casing method or a spray forming method. The sputtering target to deposit the Al film by sputtering process for a semiconductor device electrode of the present invention is adopted for an electrode of a liquid crystal display.